U.S. patent application number 13/666912 was filed with the patent office on 2013-08-22 for impedance-based adjustment of power and frequency.
This patent application is currently assigned to Lam Research Corporation. The applicant listed for this patent is Bradford J. Lyndaker, John C. Valcore, JR.. Invention is credited to Bradford J. Lyndaker, John C. Valcore, JR..
Application Number | 20130214683 13/666912 |
Document ID | / |
Family ID | 48981754 |
Filed Date | 2013-08-22 |
United States Patent
Application |
20130214683 |
Kind Code |
A1 |
Valcore, JR.; John C. ; et
al. |
August 22, 2013 |
Impedance-Based Adjustment of Power and Frequency
Abstract
Systems and methods for impedance-based adjustment of power and
frequency are described. A system includes a plasma chamber for
containing plasma. The plasma chamber includes an electrode. The
system includes a driver and amplifier coupled to the plasma
chamber for providing a radio frequency (RF) signal to the
electrode. The driver and amplifier is coupled to the plasma
chamber via a transmission line. The system further includes a
selector coupled to the driver and amplifier, a first auto
frequency control (AFC) coupled to the selector, and a second AFC
coupled to the selector. The selector is configured to select the
first AFC or the second AFC based on values of current and voltage
sensed on the transmission line.
Inventors: |
Valcore, JR.; John C.;
(Berkeley, CA) ; Lyndaker; Bradford J.; (San
Ramon, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Valcore, JR.; John C.
Lyndaker; Bradford J. |
Berkeley
San Ramon |
CA
CA |
US
US |
|
|
Assignee: |
Lam Research Corporation
Fremont
CA
|
Family ID: |
48981754 |
Appl. No.: |
13/666912 |
Filed: |
November 1, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13531491 |
Jun 22, 2012 |
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13666912 |
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13550719 |
Jul 17, 2012 |
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13531491 |
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61701560 |
Sep 14, 2012 |
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61602040 |
Feb 22, 2012 |
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61602041 |
Feb 22, 2012 |
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61602041 |
Feb 22, 2012 |
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Current U.S.
Class: |
315/111.21 |
Current CPC
Class: |
H01J 37/32146 20130101;
H01J 37/32935 20130101; H01J 37/3299 20130101; H01J 37/32183
20130101; H01J 37/32981 20130101; H01J 37/32082 20130101; H01J
37/32174 20130101; H01J 37/32165 20130101 |
Class at
Publication: |
315/111.21 |
International
Class: |
H05H 1/46 20060101
H05H001/46 |
Claims
1. A system comprising: a plasma chamber for containing plasma, the
plasma chamber including an electrode; a driver and amplifier
coupled to the plasma chamber for providing a radio frequency (RF)
signal to the electrode, the driver and amplifier coupled to the
plasma chamber via a transmission line; a selector coupled to the
driver and amplifier; a first auto frequency control (AFC) coupled
to the selector; a second AFC coupled to the selector, wherein the
selector is configured to select the first AFC or the second AFC
based on values of current and voltage sensed on the transmission
line.
2. The system of claim 1, wherein the values of current and voltage
are used to generate one or more values of gamma, wherein the
selector is configured to select the first AFC when one of the
values of gamma is greater than a first threshold and is configured
to select the second AFC when another one of the values of gamma is
greater than a second threshold.
3. The system of claim 1, wherein the selector includes a
multiplexer.
4. A system comprising: a primary generator coupled to an
electrode, the primary generator including a primary driver and
amplifier for supplying a primary radio frequency (RF) signal to
the electrode, the primary generator further including a primary
automatic frequency tuner (AFT) to provide a first primary
frequency input to the primary driver and amplifier when a pulsed
signal is in a first state, the primary AFT configured to provide a
second primary frequency input to the primary driver and amplifier
when the pulsed signal is in a second state; and a secondary
generator coupled to the electrode, the secondary generator
including a secondary driver and amplifier for supplying a
secondary RF signal to the electrode, the secondary generator
further including a first secondary AFT coupled to the secondary
driver and amplifier, the secondary generator including a second
secondary AFT coupled to the secondary driver and amplifier, the
secondary generator including a processor, the processor coupled to
the first secondary AFT and the second secondary AFT, the secondary
generator further including one or more sensors coupled to the
electrode, the one or more sensors for sensing current and voltage
transferred between the secondary generator and the electrode
during the first and second states, the processor configured to
generate parameters based on the current and voltage, the processor
configured to determine whether a first one of the parameters for
the first state exceeds a first boundary and whether a second one
of the parameters for the second state exceeds a second boundary,
the first secondary AFT configured to provide a first secondary
frequency input to the secondary driver and amplifier upon
receiving the determination that the first parameter exceeds the
first boundary, the second secondary AFT configured to provide a
second secondary frequency input to the secondary driver and
amplifier upon receiving the determination that the second
parameter exceeds the second boundary.
5. The system of claim 4, further comprising a selector coupled to
the processor for selecting the first secondary AFT or the second
secondary AFT, the selector for selecting the first secondary AFT
in response to receiving a signal from the secondary processor
indicating that the first parameter exceeds the first boundary, the
selector for selecting the second secondary AFT in response to
receiving a signal from the secondary processor indicating that the
second parameter exceeds the second boundary.
6. The system of claim 4, wherein the electrode includes a lower
electrode of a plasma chamber.
7. The system of claim 4, wherein during the first state, the
primary driver and amplifier is configured to generate the primary
RF signal having a lower frequency than that of the secondary RF
signal, wherein the primary RF signal has a higher amount of power
than the secondary RF signal.
8. The system of claim 4, wherein the processor is configured to
determine whether the pulsed signal is in the first or the second
state based on a magnitude of the pulsed signal.
9. The system of claim 4, wherein each of the first and second
parameter includes a gamma value or an impedance difference
value.
10. A system comprising: a digital pulsing source for generating a
pulsed signal; a primary generator including: a primary driver and
amplifier coupled to an electrode for supplying a primary radio
frequency (RF) signal to the electrode; one or more primary
processors coupled to the pulsing source for receiving the pulsed
signal, the one or more primary processors configured to: identify
a first one of two states of the pulsed signal and a second one of
the two states; determine to provide a primary power value to the
primary driver and amplifier when the pulsed signal is in the first
state; and determine to provide a primary frequency value of the
primary RF signal when the pulsed signal is in the first state; and
a secondary generator including: a secondary driver and amplifier
coupled to the electrode for supplying a secondary RF signal to the
electrode; one or more secondary processors coupled to the pulsing
source for receiving the pulsed signal, the one or more secondary
processors configured to: determine whether a parameter associated
with plasma exceeds a first boundary when the pulsed signal is in
the first state; determine whether the parameter exceeds a second
boundary when the pulsed signal is in the second state; determine
to provide a first secondary power value to the secondary driver
and amplifier in response to determining that the parameter exceeds
the first boundary; determine to provide a second secondary power
value to the secondary driver and amplifier in response to
determining that the parameter exceeds the second boundary;
determine to provide a first secondary frequency value to the
secondary driver and amplifier in response to determining that the
parameter exceeds the first boundary; and determine to provide a
second secondary frequency value to the secondary driver and
amplifier in response to determining that the parameter exceeds the
second boundary.
11. The system of claim 10, further comprising a selector coupled
to the one or more secondary processors for selecting the first
secondary frequency value or the second secondary frequency value,
the selector for selecting the first secondary frequency value in
response to receiving a signal from the one or more secondary
processors indicating that the first parameter exceeds the first
boundary, the selector for selecting the second secondary frequency
value in response to receiving a signal from the one or more
secondary processors indicating that the second parameter exceeds
the second boundary.
12. The system of claim 10, wherein the parameter includes a gamma
value or an impedance difference value.
13. The system of claim 10, wherein the electrode includes a lower
electrode of a plasma chamber.
14. The system of claim 10, wherein during the first state, the
primary driver and amplifier is configured to generate the primary
RF signal having a lower frequency than that of the secondary RF
signal, wherein the primary RF signal has a higher amount of power
than the secondary RF signal.
15. The system of claim 10, wherein each of the primary and
secondary frequency values are tuned.
16. The system of claim 10, wherein the one or more primary
processors determine whether the pulsed signal is in the first or
the second state based on a magnitude of the pulsed signal.
17. A method comprising: receiving a digital pulsing signal, the
digital pulsing signal having two states; receiving current and
voltage values; calculating parameters associated with plasma
impedance from the current and voltage values; determining during
the first state whether a first one of the parameters exceeds a
first boundary; providing a first frequency value and a first power
value to a radio frequency (RF) driver and amplifier upon
determining that the first parameter exceeds the first boundary;
determining during the second state whether a second one of the
parameters exceeds a second boundary; and providing a second
frequency value and a second power value to the RF driver and
amplifier upon determining that the second parameter exceeds the
second boundary.
18. The method of claim 17, wherein the method is used to process
semiconductor wafers to make integrated circuits.
19. The method of claim 17, wherein the parameters include gamma
values or impedance difference values.
20. The method of claim 17, further comprising selecting between
providing the first frequency value and the first power value or
the second frequency value and the second power value.
Description
CLAIM OF PRIORITY
[0001] The present patent application claims the benefit of and
priority, under 35 U.S.C. .sctn.119(e), to U.S. Provisional Patent
Application No. 61/701,560, filed on Sep. 14, 2012, and titled
"Impedance-based Adjustment of Power and Frequency", which is
incorporated by reference herein in its entirety for all
purposes.
[0002] The present patent application is a continuation-in-part of
and claims the benefit of and priority, under 35 U.S.C. .sctn.120,
to U.S. patent application Ser. No. 13/531,491, filed on Jun. 22,
2012, and titled "Methods and Apparatus For Controlling Plasma In A
Plasma Processing System", which is incorporated by reference
herein in its entirety for all purposes.
[0003] The U.S. patent application Ser. No. 13/531,491 claims the
benefit of and priority, under 35 U.S.C. .sctn.119(e), to U.S.
Provisional Patent Application No. 61/602,040, filed on Feb. 22,
2012, and titled "Frequency Enhanced Impedance Dependent Power
Control For Multi-frequency Pulsing", which is incorporated by
reference herein in its entirety for all purposes.
[0004] The U.S. patent application Ser. No. 13/531,491 claims the
benefit of and priority, under 35 U.S.C. .sctn.119(e), to U.S.
Provisional Patent Application No. 61/602,401, filed on Feb. 23,
2012, which is incorporated by reference herein in its entirety for
all purposes.
[0005] The present patent application is a continuation-in-part of
and claims the benefit of and priority, under 35 U.S.C. .sctn.120,
to U.S. patent application Ser. No. 13/550,719, filed on Jul. 17,
2012, and titled "Methods and Apparatus For Synchronizing RF Pulses
In A Plasma Processing System", which is incorporated by reference
herein in its entirety for all purposes.
[0006] The U.S. patent application Ser. No. 13/550,719 claims the
benefit of and priority, under 35 U.S.C. .sctn.119(e), to U.S.
Provisional Patent Application No. 61/602,041, filed on Feb. 22,
2012, and titled "Frequency Enhanced Impedance Dependent Power
Control For Multi-frequency Pulsing", which is incorporated by
reference herein in its entirety for all purposes.
CROSS-REFERENCE TO RELATED APPLICATIONS
[0007] The present patent application is related to application
Ser. No. 13/620,386, filed on Sep. 14, 2012, titled "State-Based
Adjustment of Power and Frequency", which is incorporated by
reference herein in its entirety for all purposes.
FIELD
[0008] The present embodiments relate to improving response time to
a change in plasma impedance and/or to improving accuracy in
stabilizing plasma, and more particularly, to apparatus, methods,
and computer programs for impedance-based adjustment of power and
frequency.
BACKGROUND
[0009] In some plasma processing systems, multiple radio frequency
(RF) signals are provided to one or more electrodes within a plasma
chamber. The RF signals help generate plasma within the plasma
chamber. The plasma is used for a variety of operations, e.g.,
clean substrate placed on a lower electrode, etch the substrate,
etc.
[0010] Between a driver and amplifier system that generates a radio
frequency (RF) signal and the plasma chamber, an impedance matching
circuit is usually placed. The impedance matching circuit matches
an impedance of a load, e.g., plasma within the plasma chamber,
with an impedance of a source, e.g., the driver and amplifier
system that generates the RF signal. However, in certain
situations, the impedance matching is not quick enough to respond
to a change in the plasma impedance.
[0011] Moreover, although some systems are quick enough to respond
to the change, these systems may not result in accurate adjustment
of power and/or frequency to stabilize the plasma.
[0012] It is in this context that embodiments described in the
present disclosure arise.
SUMMARY
[0013] Embodiments of the disclosure provide apparatus, methods and
computer programs for state-based adjustment of power and
frequency. It should be appreciated that the present embodiments
can be implemented in numerous ways, e.g., a process, an apparatus,
a system, a device, or a method on a computer-readable medium.
Several embodiments are described below.
[0014] In an embodiment, a system includes a plasma chamber for
containing plasma. The plasma chamber includes an electrode. The
system includes a driver and amplifier (DA) system that is coupled
to the plasma chamber for providing a radio frequency (RF) signal
to the electrode. The DA system is coupled to the plasma chamber
via a transmission line. The system further includes a selector
coupled to the DA system, a first auto frequency control (AFC)
coupled to the selector, and a second AFC coupled to the selector.
The selector is configured to select the first AFC or the second
AFC based on values of current and voltage sensed on the
transmission line.
[0015] In one embodiment, a system includes a primary generator
coupled to an electrode. The primary generator includes a primary
driver and amplifier for supplying a primary radio frequency (RF)
signal to the electrode. The primary generator further includes a
primary automatic frequency tuner (AFT) to provide a first primary
frequency input to the primary driver and amplifier when a pulsed
signal is in a first state. The primary AFT is configured to
provide a second primary frequency input to the primary driver and
amplifier when the pulsed signal is in a second state. The system
further includes a secondary generator coupled to the
electrode.
[0016] In this embodiment, the secondary generator includes a
secondary driver and amplifier for supplying a secondary RF signal
to the electrode. The secondary generator further includes a first
secondary AFT coupled to the secondary driver and amplifier. The
secondary generator includes a second secondary AFT coupled to the
secondary driver and amplifier. The secondary generator also
includes a processor, which is coupled to the first secondary AFT
and the second secondary AFT. The secondary generator further
includes a sensor coupled to the electrode. The sensor is used for
sensing current and voltage transferred between the secondary
generator and the electrode during the first and second states. The
processor is configured to generate parameters based on the current
and voltage and is configured to determine whether a first one of
the parameters for the first state exceeds a first boundary and
whether a second one of the parameters for the second state exceeds
a second boundary. The first secondary AFT is configured to provide
a first secondary frequency input to the secondary driver and
amplifier upon receiving the determination that the first parameter
exceeds the first boundary and the second secondary AFT configured
to provide a second secondary frequency input to the secondary
driver and amplifier upon receiving the determination that the
second parameter exceeds the second boundary.
[0017] In an embodiment, a system including a digital pulsing
source for generating a pulsed signal is described. The system
includes a primary generator. The primary generator includes a
primary driver and amplifier coupled to an electrode for supplying
a primary radio frequency (RF) signal to the electrode. The primary
generator also includes one or more primary processors coupled to
the pulsing source for receiving the pulsed signal. The one or more
primary processors are configured to identify a first one of two
states of the pulsed signal and a second one of the two states,
determine to provide a primary power value to the primary driver
and amplifier when the pulsed signal is in the first state, and
determine to provide a primary frequency value of the primary RF
signal when the pulsed signal is in the first state.
[0018] In this embodiment, the system further includes a secondary
generator, which includes a secondary driver and amplifier coupled
to the electrode for supplying a secondary RF signal to the
electrode. The secondary generator further includes one or more
secondary processors coupled to the pulsing source for receiving
the pulsed signal. The one or more secondary processors are
configured to determine whether a parameter associated with plasma
exceeds a first boundary when the pulsed signal is in the first
state, determine whether the parameter exceeds a second boundary
when the pulsed signal is in the second state, and determine to
provide a first secondary power value to the secondary driver and
amplifier in response to determining that the parameter exceeds the
first boundary. The one or more secondary processors are further
configured to determine to provide a second secondary power value
to the secondary driver and amplifier in response to determining
that the parameter exceeds the second boundary, determine to
provide a first secondary frequency value to the secondary driver
and amplifier in response to determining that the parameter exceeds
the first boundary, and determine to provide a second secondary
frequency value to the secondary driver and amplifier in response
to determining that the parameter exceeds the second boundary.
[0019] In an embodiment, a method includes receiving a digital
pulsing signal, which has two states. The method includes receiving
current and voltage values, calculating parameters associated with
plasma impedance from the current and voltage power values, and
determining during the first state whether a first one of the
parameters exceeds a first boundary. The method also includes
providing a first frequency value and a first power value to a
radio frequency (RF) driver and amplifier upon determining that the
first parameter exceeds the first boundary, determining during the
second state whether a second one of the parameters exceeds a
second boundary, and providing a second frequency value and a
second power value to the RF driver and amplifier upon determining
that the second parameter exceeds the second boundary.
[0020] Some advantages of the above-described embodiments include
providing an accurate power and/or frequency value to stabilize
plasma, e.g., to reduce a difference between an impedance of a
source, e.g., RF driver and amplifier, and a load, e.g., plasma.
The frequency and/or power value is accurate when the power and/or
frequency value is generated based on a change in plasma impedance.
For example, forward power and reflected power are measured and are
used to generate a gamma value. It is determined whether the gamma
value exceeds a threshold and if so, the power and/or frequency
value is changed to stabilize plasma.
[0021] Other advantages of embodiments include reducing an amount
of time to achieve stability in plasma. A training routine is used
to determine frequency and/or power values to apply to a driver and
amplifier system. The power and/or frequency values correspond to a
gamma value that is also determined during the training routine.
The training routine saves time during production, e.g., time for
cleaning substrates, time for etching substrates, time for
deposition material on substrates, etc. For example, during
production, when it is determined that the gamma value exceeds a
threshold, the power and/or frequency values are applied to the
driver and amplifier system without a need to tune the power and/or
frequency values.
[0022] Other aspects will become apparent from the following
detailed description, taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The embodiments may best be understood by reference to the
following description taken in conjunction with the accompanying
drawings.
[0024] FIG. 1 is a block diagram of an embodiment of a system for
changing a state based on plasma impedance, in accordance with an
embodiment described in the present disclosure.
[0025] FIG. 2 is an embodiment of a table showing a change in
states based on whether a gamma value is greater than a first
threshold or a second threshold, in accordance with an embodiment
described in the present disclosure.
[0026] FIG. 3 shows an embodiment of a graph, which is a plot of a
forward power versus time of two RF signals during a training
routine, in accordance with an embodiment described in the present
disclosure.
[0027] FIG. 4 is an embodiment of a flowchart of a training
routine, in accordance with an embodiment described in the present
disclosure.
[0028] FIG. 5 is a diagram of an embodiment of a system for
changing a state based on plasma impedance, where the power
controllers and/or the frequency tuners do not provide non-zero
values, in accordance with an embodiment described in the present
disclosure.
[0029] FIG. 6A shows graphs with two radio frequency (RF) signals
in which one of the RF signals has a constant value or varying
values, in accordance with an embodiment described in the present
disclosure.
[0030] FIG. 6B shows graphs with two RF signals in which both the
RF signals have varying values, in accordance with an embodiment
described in the present disclosure.
[0031] FIG. 7A shows graphs with three RF signals in which one of
the RF signals has a constant value and another one of the RF
signals has a constant value or varying values, in accordance with
an embodiment described in the present disclosure.
[0032] FIG. 7B shows graphs with three RF signals in which one of
the RF signals a constant value and the remaining two RF signals
have varying values, in accordance with an embodiment described in
the present disclosure.
[0033] FIG. 7C shows graphs with three RF signals in which one of
the RF signals has a constant value or varying values and the
remaining two RF signals have varying values, in accordance with an
embodiment described in the present disclosure.
[0034] FIG. 7D shows graphs with all three RF signals have varying
values, in accordance with an embodiment described in the present
disclosure.
[0035] FIG. 7E shows graphs with three RF signals in which one of
the RF signals has a constant value or varying values and the
remaining RF signals have varying values, in accordance with an
embodiment described in the present disclosure.
[0036] FIG. 7F shows graphs with all three RF signals have varying
values, in accordance with an embodiment described in the present
disclosure.
[0037] FIG. 8 is a block diagram of an embodiment of a system for
selecting between auto frequency tuners (AFTs) based on whether a
gamma value is greater than a first threshold or a second
threshold, in accordance with an embodiment described in the
present disclosure.
[0038] FIG. 9 is a flowchart of an embodiment of a method for
adjusting a frequency and/or power of a 60 MHz driver and amplifier
to achieve a state S1 or S0 of a 60 MHz generator, in accordance
with an embodiment described in the present disclosure.
[0039] FIG. 10 shows an embodiment of a graph of normalized RF
variables versus time for implementing RF tuning by a dependent RF
generator for optimal production time power delivery during
independent (IP) RF signal pulsing, in accordance with one
embodiment described in the present disclosure.
[0040] FIG. 11 is an embodiment of a flowchart of a method for
implementing frequency tuning by a dependent RF generator for
optimal power delivery during pulsing, in accordance with an
embodiment described in the present disclosure.
DETAILED DESCRIPTION
[0041] The following embodiments describe systems and methods for
impedance-based adjustment of power and frequency. It will be
apparent that the present embodiments may be practiced without some
or all of these specific details. In other instances, well known
process operations have not been described in detail in order not
to unnecessarily obscure the present embodiments.
[0042] FIG. 1 is a block diagram of an embodiment of a system 180
for changing a state based on plasma impedance. A 2 megahertz (MHz)
radio frequency (RF) driver and amplifier (DA) system supplies RF
power via an impedance matching circuit 182 to a lower electrode
104 of a plasma chamber 102. Similarly, a 60 MHz DA system supplies
RF power via an impedance matching circuit 186 to the lower
electrode 104. It should be noted that in one embodiment, instead
of the 60 MHz source, a 27 MHz source is used to provide RF power
to the lower electrode 104. Moreover, it should be noted that the
values 2 MHz, 27 MHz, and 60 MHz are provided as examples and are
not limiting. For example, instead of the 2 MHz DA system, a 2.5
MHz DA system may be used and instead of the 60 MHz DA system, a 65
MHz DA system may be used. In another embodiment, in addition to
the 2 MHz source and the 60 MHz sources, the 27 MHz source is used
to provide RF power to the lower electrode 104.
[0043] An impedance matching circuit includes electric circuit
components, e.g., inductors, capacitors, etc. to match an impedance
of a power source coupled to the impedance matching circuit with an
impedance of a load coupled to the impedance matching circuit. For
example, the impedance matching circuit 182 matches an impedance of
the 2 MHz DA system with an impedance of plasma generated within
the plasma chamber 102. As another example, an impedance matching
circuit 186 matches an impedance of the 60 MHz DA system with an
impedance of plasma generated within the plasma chamber 102. As yet
another example, the impedance matching circuit 182 matches an
impedance of the 2 MHz DA system with an impedance of a portion,
e.g., the plasma and the lower electrode 104, of the plasma chamber
102. In one embodiment, an impedance matching circuit is tuned to
facilitate a match between an impedance of an RF DA system coupled
to the impedance matching circuit and an impedance of a load. An
impedance match between a power source and a load reduces chances
of power being reflected from the load towards the power
source.
[0044] The plasma chamber 102 includes the lower electrode 104, an
upper electrode 110, and other components (not shown), e.g., an
upper dielectric ring surrounding the upper electrode 110, a lower
electrode extension surrounding the upper dielectric ring, a lower
dielectric ring surrounding the lower electrode, a lower electrode
extension surrounding the lower dielectric ring, an upper plasma
exclusion zone (PEZ) ring, a lower PEZ ring, etc. The upper
electrode 110 is located opposite to and facing the lower electrode
104. A substrate 108, e.g., a semiconductor wafer, is supported on
an upper surface 106 of the lower electrode 104. Integrated
circuits, e.g., application specific integrated circuit (ASIC),
programmable logic device (PLD), etc. are developed on the
substrate 108 and the integrated circuits are used in a variety of
devices, e.g., cell phones, tablets, smart phones, computers,
laptops, networking equipment, etc. The lower electrode 104 is made
of a metal, e.g., anodized aluminum, alloy of aluminum, etc. Also,
the upper electrode 110 is made of a metal, e.g., aluminum, alloy
of aluminum, etc.
[0045] In one embodiment, the upper electrode 110 includes a hole
that is coupled to a central gas feed (not shown). The central gas
feed receives one or more process gases from a gas supply (not
shown). Examples of a process gases include an oxygen-containing
gas, such as O.sub.2. Other examples of a process gas include a
fluorine-containing gas, e.g., tetrafluoromethane (CF.sub.4),
sulfur hexafluoride (SF.sub.6), hexafluoroethane (C.sub.2F.sub.6),
etc. The upper electrode 110 is grounded. The lower electrode 104
is coupled to the 2 MHz RF DA system via the impedance matching
circuit 182 and to the 60 MHz RF DA system via the impedance
matching circuit 186.
[0046] When the process gas is supplied between the upper electrode
110 and the lower electrode 104 and when a DA system, e.g., the 2
MHz DA system and/or the 60 MHz DA system, supplies power via a
corresponding impedance matching circuit to the lower electrode
104, the process gas is ignited to generate plasma within the
plasma chamber 102. For example, the 2 MHz DA system supplies power
via the impedance matching circuit 182 to ignite the process gas to
generate plasma.
[0047] A tool user interface (UI) 190 on a computer (not shown) is
used to generate a transistor-transistor logic (TTL) signal 112,
which is a digital pulsing signal. In one embodiment, the computer
includes a TTL circuit. As used herein, instead of a computer, a
processor, a controller, an ASIC, or a PLD is used, and these terms
are used interchangeably herein. The TTL signal 112 includes states
S1 and S0. The TTL signal 112 has a 50% duty cycle. In one
embodiment, the TTL signal 112 has a duty cycle ranging from 5% to
95%. An example of the state S1 includes an on state, a state
having a value of 1, or a high state. An example of the state S0
includes an off state, a state having a value of 0, or a low state.
The high value is greater than the low value.
[0048] In another embodiment, instead of the computer, a clock
oscillator, e.g., a crystal oscillator, is used to generate an
analog clock signal, which is converted by an analog-to-digital
converter into a digital signal similar to the TTL signal 112. For
example, a crystal oscillator is made to oscillate in an electric
field by applying a voltage to an electrode near or on the crystal
oscillator.
[0049] The TTL signal 112 is sent to a digital signal processor
(DSP) 140 and another DSP 150. The DSP 140 receives the TTL signal
112 and identifies the states S0 and S1 of the TTL signal 112. For
example, the DSP 140 distinguishes between the states S0 and S1. As
another example, the DSP 140 determines that the TTL signal 112 has
a first magnitude during a first set of time periods and has a
second magnitude during a second set of time periods. The DSP 140
determines that the TTL signal 112 has the state S1 during the
first set of time periods and has the state S0 during the second
set of time periods. As yet another example, the DSP 140 compares a
magnitude of the TTL signal 112 with a pre-stored value to
determine that the magnitude of the TTL signal 112 is greater than
the pre-stored value during the first set of time periods and that
the magnitude during the state S0 of the TTL signal 112 is not
greater than the pre-stored value during the second set of time
periods. In the embodiment in which the clock oscillator is used,
the DSP 140 receives an analog clock signal from the clock
oscillator, converts the analog signal into a digital form, and
then identifies the two states S0 and S1.
[0050] The DSP 140 stores the identified states S0 and S1 in memory
locations of one or more memory devices within the DSP. Examples of
a member device include a random access memory (RAM) and a
read-only memory (ROM). A memory device may be a flash memory, a
hard disk, a storage device, a computer-readable medium, etc.
[0051] The DSP 140 provides the identified state S1 from
corresponding memory locations to an auto frequency tuner (AFT) 114
and to a power controller 142. For example, the DSP 140 indicates
to the AFT 114 and the power controller 142 that the TTL signal 112
is in the state S1 between times t1 and t2 of a duty cycle. The
terms tuner and controller are used interchangeably herein. An
example of an AFT is provided in U.S. Pat. No. 6,020,794, which is
incorporated by reference herein in its entirety.
[0052] In one embodiment, instead of a controller or a tuner, a
control logic block, e.g., a computer program, that is executed by
a processor is used. For example, each AFT of a generator is a
logic block that is executed by a processor of the generator. As
another example, each power controller of a generator is a logic
block that is executed by a processor of the generator. A computer
program is embodied in a non-transitory computer-readable medium,
examples of which are provided below.
[0053] The AFT 114 determines a frequency value based on a state of
the TTL signal 112 and the power controller 142 determines a power
value based on a state of the TTL signal 112. For example, the AFT
114 determines that a frequency value F11 is to be provided to the
2 MHz DA system when the state of the TTL signal 112 is S1 and the
power controller 142 determines that a power value P11 is to be
provided to the 2 MHz DA system when the state of the TTL signal
112 is S1.
[0054] When the state of the TTL signal 112 is S1, the power
controller 142 provides the power value of P11 to the 2 MHz DA
system. During the state S1 of the TTL signal 112, the AFT 114
provides the frequency value of F11 to the 2 MHz DA system.
[0055] The 2 MHz DA system receives the frequency value of F11 and
the power value of P11 during the state S1. Upon receiving the
values F11 and P11, the 2 MHz DA system generates an RF signal
having the frequency F11 and the RF signal has the power value of
P11.
[0056] In one embodiment, an RF DA system includes a driver
followed by an amplifier. The amplifier supplies forward power via
a transmission line to the plasma chamber 102. For example, the
amplifier of the 2 MHz DA system supplies forward power having a
power value that is proportional, e.g., same as, multiple of, etc.
to the power value P11 and having the frequency value F11 via a
transmission line 230 and the impedance matching circuit 182 to the
plasma chamber 102.
[0057] When the TTL signal 112 transitions from the state S1 to the
state S1 and when the 2 MHz DA system supplies forward power having
the power value proportional to the power value P11 and having the
frequency value F11 to the plasma chamber 102, impedance with the
plasma chamber 102 changes. When the impedance within the plasma
chamber 102 changes as a result of transition of the TTL signal 112
from the state S1 to the state S0, a sensor 212 of a 60 MHz
generator 276 measures forward power and reflected power, which is
RF power reflected from the plasma of the plasma chamber 102, on a
transmission line 232. The sensor 212 provides the measurement of
the forward and reflected powers to an analog-to-digital (ADC)
converter 222, which converts the measurements from an analog
format to a digital format. The digital values of the forward and
reflected powers are provided to a DSP 150. In an embodiment, a DSP
includes an ADC. It should further be noted that in one embodiment,
the DSP 150 lacks reception of the TTL signal 112. Rather, in this
embodiment, the DSP 150 receives another digital pulsed signal that
may not be synchronous with the TTL signal 112. In one embodiment,
the other digital pulsed signal received by the DSP 150 is
synchronous with the TTL signal 112.
[0058] During the state S1 of the TTL signal 112, e.g., immediately
after the state transition from S1 to S0 of the TTL signal 112, the
DSP 150 calculates a relationship, e.g., a square root of a ratio
of the digital reflected power signal and the digital forward power
signal, a voltage standing wave ratio (VSWR), etc., during the
state S1 to generate a first gamma value. A gamma value of 1
indicates a high degree of mismatch between impedances of a source
and a load and a gamma value of 0 indicates a low degree of
mismatch between impedances of a source and a load. If a gamma
value is zero, power delivery to the plasma chamber 102 is deemed
highly efficient. If the gamma value is 1, the power delivery is
deemed highly inefficient. The VSWR is calculated as being equal to
a ratio of RC-1 and RC+1, where RC is a reflection coefficient.
[0059] The DSP 150 determines whether the first gamma value is
greater than a first threshold. When the DSP 150 determines that
the first gamma value is greater than the first threshold, the DSP
150 indicates the same to an AFT 118 and to a power controller 152.
The AFT 118 determines a frequency value F21 corresponding to the
first gamma value and provides the frequency value F21 to the 60
MHz DA system. Moreover, the power controller 152 determines a
power value P21 corresponding to the first gamma value and provides
the power value P21 corresponding to the first gamma value to the
60 MHz DA system. For example, the AFT 118 stores within a memory
device, a table that maps the first gamma value with the frequency
value F21 and the power controller 152 stores within a memory
device a mapping between the power value P21 and the first gamma
value.
[0060] In one embodiment, the AFT 118 determines each of the
frequency value F21 and the power value P21 as corresponding to the
first threshold. For example, the AFT 118 stores within a memory
device, a table that maps the first threshold with the frequency
value F21 and the power controller 152 stores within a memory
device a mapping between the power value P21 and the first
threshold.
[0061] The 60 MHz DA system receives the frequency value of F21 and
the power value of P21 during the state S1 of the TTL signal 112.
Upon receiving the values F21 and P21, the 60 MHz DA system
generates an RF signal having the frequency F21 and the RF signal
has the power value of P21. For example, an amplifier of the 60 MHz
DA system supplies forward power having a power value that is
proportional, e.g., same as, multiple of, etc. to the power value
P21 and having the frequency value F21 via the transmission line
232 and the impedance matching circuit 186 to the plasma chamber
102.
[0062] When the state of the TTL signal 112 changes from S1 to S0,
no power value and no frequency value is provided to the 2 MHz DA
system. During the state S0, no frequency value is provided to the
2 MHz DA system. The 2 MHz DA system does not receive any frequency
and power values, e.g., receives the frequency value of 0 and the
power value of 0, during the state S0. Upon not receiving power and
frequency values, the 2 MHz DA system generates RF power at a
frequency of zero and RF power having a power value of zero. The
amplifier of the 2 MHz DA system does not supply forward power,
e.g., supplies forward power having a power value of zero and
having a frequency value of zero, via the transmission line 230 and
the impedance matching circuit 182 to the plasma chamber 102.
[0063] Moreover, when the state of the TTL signal 112 changes to
the state S0 from the state S1, the impedance of plasma within the
plasma chamber 102 changes. Again, during the state S0 of the TTL
signal 112, e.g., immediately after the transition from the state
S1 to the state S0 of the TTL signal 112, the sensor 212 determines
the forward and reflected powers on the transmission line 232 and
provides the measured forward and reflected powers to an ADC 222.
The ADC 222 converts the measured forward and reflected powers from
analog format to a digital format. The DSP 150 receives the digital
forward and reflected powers from the ADC 222 and calculates a
second gamma value from the forward and reflected powers.
[0064] The DSP 150 compares the second gamma value to a second
threshold and determines whether the second gamma value is greater
than the second threshold. When the DSP 150 determines that the
second gamma value is greater than the second threshold, the DSP
150 indicates the same to an AFT 118 and to the power controller
152. The AFT 118 determines a frequency value F20 corresponding to
the second gamma value and provides the frequency value F20 to the
60 MHz DA system. Moreover, the power controller 152 determines a
power value P20 corresponding to the second gamma value and
provides the power value P20 corresponding to the second gamma
value to the 60 MHz DA system. For example, the AFT 118 stores
within a memory device, a table that maps the second gamma value
with the frequency value F20 and the power controller 152 stores
within a memory device a mapping between the power value P20 and
the second gamma value.
[0065] In one embodiment, the AFT 118 determines each of the
frequency value F20 and the power value P20 as corresponding to the
second threshold. For example, the AFT 118 stores within a memory
device, a table that maps the second threshold with the frequency
value F20 and the power controller 152 stores within a memory
device a mapping between the power value P20 and the second
threshold.
[0066] The 60 MHz DA system receives the frequency value of F20 and
the power value of P20 during the state S0 of the TTL signal 112.
Upon receiving the values F20 and P20, the 60 MHz DA system
generates an RF signal having the frequency F20 and the RF signal
has the power value of P20. For example, an amplifier of the 60 MHz
DA system supplies forward power having a power value that is
proportional, e.g., same as, multiple of, etc. to the power value
P20 and having the frequency value F20 via the transmission line
232 and the impedance matching circuit 186 to the plasma chamber
102.
[0067] The use of measurement of forward and reflected powers to
change RF power provided by the 60 MHz DA system results in plasma
stability. Also, the plasma stability is based on real-time
measurement of forward and reflected powers. This real-time
measurement provides accuracy in stabilizing the plasma.
[0068] In one embodiment, during one or both the states S1 and S0,
a sensor 210 of the 2 MHz generator 274 senses RF power reflected
from the plasma of the plasma chamber 102 on the transmission line
230. Moreover, during one or both the states S1 and S0, the sensor
210 senses forward power on the transmission line 230 when the
forward power is sent from the 2 MHz RF DA system via the
transmission line 230 to the plasma chamber 102. Similarly, during
one or both the states S1 and S0, the sensor 212 senses power
reflected from the plasma of the plasma chamber 102. The reflected
power sensed by the sensor 212 is reflected on the transmission
line 232 from the plasma of the plasma chamber 102. Moreover,
during one or both the states S1 and S0 of the TTL signal 112, the
sensor 212 senses forward power on the transmission line 232 when
the forward power is sent from the 60 MHz RF DA system via the
transmission line 232 to the plasma chamber 102.
[0069] In this embodiment, an analog-to-digital converter (ADC) 220
converts the measured reflected and forward powers sensed by the
sensor 210 from an analog form to a digital form and the ADC 222
converts the measured reflected and forward powers sensed by the
sensor 212 from an analog to a digital form. During one or both the
states S1 and S0, the DSP 140 receives the digital values of the
reflected power signal and the forward power signal sensed by the
sensor 210 and the DSP 150 receives the digital value of the
reflected power signal and the forward power signal sensed by the
sensor 212.
[0070] Furthermore, in this embodiment, a gamma value that is
generated from the digital values of the forward and reflected
powers on the transmission line 230 during the state S1 is sent
from the DSP 140 to the AFT 114 and a gamma value that is generated
from the digital values of the forward and reflected powers on the
transmission line 232 during the state S1 is sent from the DSP 150
to the AFT 118. During the state S1, the AFT 114 determines a
frequency value based on the value of gamma received from the DSP
140 and the AFT 118 determines a frequency value based on the value
of gamma received from the DSP 150. During the state S1, the AFT
114 adjusts the frequency value of F11 based on the frequency value
that is generated based on the gamma value and provides the
adjusted frequency value to the 2 MHz DA system. Moreover, during
the state S1, the AFT 118 adjusts the frequency value of F21 based
on the frequency value that is generated based on the gamma value
and provides the adjusted frequency value to the 60 MHz DA
system.
[0071] Moreover, in the same embodiment, during the state S1, the
power controller 142 determines a power value based on the value of
gamma received from the DSP 140 and the power controller 152
determines a power value based on the value of gamma received from
the DSP 150. During the state S1, the power controller 142 adjusts
the power value of P11 based on the power value that is generated
based on the gamma value and provides the adjusted power value to
the 2 MHz DA system. Moreover, during the state S1, the power
controller 152 adjusts the power value of P21 based on the power
value that is generated based on the gamma value and provides the
adjusted power value to the 60 MHz DA system.
[0072] Further, in this embodiment, during the state S1, the 2 MHz
DA system generates a power signal having the adjusted frequency
value received from the AFT 114 and having the adjusted power value
received from the power controller 142, and supplies the power
signal via the impedance matching circuit 182 to the plasma chamber
102. Similarly, during the state S1, the 60 MHz DA system generates
a power signal having the adjusted frequency value received from
the AFT 118 and having the adjusted power value received from the
power controller 152, and supplies the power signal via the
impedance matching circuit 186 to the plasma chamber 102.
[0073] Furthermore, in the same embodiment, during the state S0,
there is no provision of power and frequency values to the 2 MHz DA
system and there is no use of a gamma value generated during the
state S0 to adjust the zero frequency and power values of the 2 MHz
DA system. A gamma value that is generated from the digital values
of the forward and reflected powers on the transmission line 232
during the state S0 is sent from the DSP 150 to the AFT 120. The
AFT 120 determines a frequency value based on the value of gamma
received from the DSP 150. During the state S0, the AFT 120 adjusts
the frequency value of F20 based on the frequency value that is
generated from the gamma value and provides the adjusted frequency
value to the 60 MHz DA system. Moreover, during the state S0, the
power controller 154 determines a power value based on the value of
gamma received from the DSP 150. During the state S0, the power
controller 154 adjusts the power value of P20 based on the power
value that is generated based on the gamma value and provides the
adjusted power value to the 60 MHz DA system. During the state S0,
the 60 MHz DA system generates a power signal having the adjusted
frequency value received from the AFT 120 and having the adjusted
power value received from the power controller 154, and supplies
the power signal via the impedance matching circuit 186 to the
plasma chamber 102.
[0074] It should be noted that in this embodiment, a difference
between an adjusted value that is generated by adjusting a value
and the value is smaller than a difference between another power or
frequency value that is generated by using the first or second
threshold. For example, a difference between the adjusted power
value generated from the power value P21 and the power value P21 is
less than a difference between the power values P21 and P20. As
another example, a difference between the adjust frequency value
generated from the frequency value F20 and the frequency value F20
is less than a difference between the frequency values F21 and
F20.
[0075] The power controller 142, the AFT 114, and the DSP 140 are
parts of a generator controller 270. The generator controller 270,
the ADC 220, the sensor 210, and the 2 MHz DA system are parts of a
2 MHz generator 274. Similarly, the power controller 152, the power
controller 154, the AFTs 118 and 120, and the DSP 150 are parts of
a generator controller 272. The generator controller 272, the ADC
222, the sensor 212, and the 60 MHz DA system are parts of the 60
MHz generator 276.
[0076] In one embodiment, the system 180 excludes the impedance
matching circuits 182 and/or 186. In an embodiment, a single
controller is used instead of the power controller 142 and the AFT
114, a single controller is used instead of the power controller
152 and the AFT 118, and a single controller is used instead of the
power controller 154 and the AFT 120.
[0077] In the embodiment in which the 27 MHz DA system is used in
addition to using the 2 and 60 MHz power supplies, a 27 MHz
generator is similar to the 60 MHz generator 276 except that the 27
MHz generator includes the 27 MHz DA system instead of the 60 MHz
DA system. The 27 MHz generator is coupled to the lower electrode
104 of the plasma chamber 102 via an impedance matching circuit
(not shown) and a transmission line (not shown). Moreover, the 27
MHz DA system is coupled to a digital pulsed signal source, other
than the Tool UI 112, and a digital pulsed signal generated by the
digital pulsed signal source may not be synchronous with the TTL
signal 112. An example of a digital pulsed signal source includes a
clock oscillator or a computer that includes a TTL circuit that
generates a TTL signal. In one embodiment, the digital pulsed
signal generated by the digital pulsed signal source is synchronous
with the TTL signal 112. The 27 MHz generator includes two power
controllers, two AFTs, a DSP, an ADC, a sensor, and the 27 MHz DA
system.
[0078] In an embodiment, the first threshold and the second
threshold are generated during a training routine, e.g., a learning
process. During the training routine, when the 2 MHz DA system
changes its RF power signal from a low power value to a high power
value, there is an impedance mismatch between one or more portions,
e.g., plasma, etc., within the plasma chamber 102 and 60 MHz DA
system. The high power value is higher than the low power value.
The 2 MHz DA system changes a state of its RF power signal from the
low power value to the high power value when a state of the TTL
signal 112 or a clock signal supplied to the 2 MHz RF DA system
changes from S0 to S1. In this case, the 60 MHz DA system has its
frequency and power tuned when the 2 MHz DA system starts supplying
power at the high power value. To reduce the impedance mismatch,
the 60 MHz DA system starts tuning, e.g., converging, to a power
value and to a frequency value. The convergence may be determined
by the DSP 150 based on a standard deviation or another technique.
To allow the 60 MHz DA system more time to converge to the power
value and to the frequency value, the 2 MHz DA system is kept at
the high power value for an extended period of time than a usual
period of time. The usual period of time is an amount of time in
which the impedance mismatch is not reduced, e.g., removed. An
example of the usual period of time is equal to half cycle of the
TTL signal 112. When the 60 MHz DA system converges to the power
value and the frequency value, the converged power value is stored
as the power value P21 within the power controller 152 and the
converged frequency value is stored as the frequency value F21
within the AFT 118. The first threshold is generated from the power
value P21 during the training routine and the first gamma value
corresponds to the frequency value F21. For example, the sensor 212
measures the forward power value and a reflected power value during
the training routine. The sensor 212 measures the forward and
reflected power values during the training routine when the
frequency of the 60 MHz signal is F21. The ADC 222 converts the
measured forward and reflected values from an analog format to a
digital format. The DSP 150 receives the digital forward power
value of P21 and the digital reflected power value from the ADC 222
and generates the first threshold from the power value P21 and the
digital reflected power value measured during the training
routine.
[0079] Similarly, during the training routine, the power value P20
and the frequency values F20 are generated when the 2 MHz DA system
changes its RF power signal from the high power value to the low
power value. The power value P20 is stored in the power controller
154 and the frequency value F20 is stored in the AFT 120. Also, the
power value P20 is used to generate the second threshold during the
training routine in a similar manner in which the first threshold
is generated from the power value P21. The second threshold
corresponds to the frequency value F20. For example, when the power
value of the 60 MHz signal is determined to be P20, the frequency
value of the 60 MHz signal is F20.
[0080] In an embodiment, instead of the DSP 150, the AFT 118 and
the power controller 152 determine whether the first gamma value is
greater than the first threshold. In this embodiment, the DSP 150
provides the first gamma value to the AFT 118 and the power
controller 152. When the AFT 118 determines that the first gamma
value is greater than the first threshold, the AFT 118 determines
the frequency value F21 corresponding to the first gamma value and
provides the frequency value F21 to the 60 MHz DA system. Moreover,
when the power controller 152 determines that the first gamma value
is greater than the first threshold, the power controller 152
determines the power value P21 corresponding to the first gamma
value and provides the power value P21 to the 60 MHz DA system.
[0081] Moreover, in this embodiment, instead of the DSP 150, the
AFT 120 and the power controller 154 determine whether the second
gamma value is greater than the second threshold. In this
embodiment, the DSP 150 provides the second gamma value to the AFT
120 and the power controller 154. When the AFT 120 determines that
the second gamma value is greater than the second threshold, the
AFT 120 determines the frequency value F20 corresponding to the
second gamma value and provides the frequency value F20 to the 60
MHz DA system. Moreover, when the power controller 154 determines
that the second gamma value is greater than the second threshold,
the power controller 154 determines the power value P20
corresponding to the second gamma value and provides the power
value P20 to the 60 MHz DA system.
[0082] In an embodiment, instead of the sensor 212 sensing the
forward and reflected powers, complex voltage and current are
sensed and gamma is generated from the sensed values voltage and
current. For example, one or more sensors, e.g., voltage sensors,
current sensors, etc. sense current and voltage on the transmission
line 232, and provide the sensed current and voltage values as
complex values to the DSP 150. The DSP 150 calculates forward and
reflected powers from the sensed current and voltage values, and
generates gamma values from the forward and reflected powers.
[0083] In one embodiment, instead of the sensor 212 sensing the
forward and reflected powers, during the state S1 of the TTL signal
106, a first comparator compares voltage or current, which is
reflected on the transmission line 232, to determine whether the
voltage or current is greater than a first pre-determined value.
During the state S1 of the TTL signal 106, when the voltage or
current is greater than the first pre-determined value, the first
comparator provides a first signal to the DSP 150 and when the
voltage or current is not greater than the first pre-determined
value, the comparator provides a second signal to the DSP 150. In
response to receiving the first signal, the DSP 150 identifies that
the voltage or current is greater than the first pre-determined
value and in response to receiving the second signal, the DSP 150
identifies that the voltage or current does not exceed the first
pre-determined value. When the DSP 150 identifies that the voltage
or current exceeds the first pre-determined value, the DSP 150
determines the frequency value F21 corresponding to the first
pre-determined value and provides the frequency value F21 to the
AFT 118. Moreover, upon receiving the indication that the voltage
or current exceeds the first pre-determined value, the DSP 150
determines the power value P21 corresponding to the first
pre-determined value and provides the power value P21 to the power
controller 152. The comparator is coupled to the DSP 150.
[0084] In this embodiment, during the state S0 of the TTL signal
106, the comparator compares voltage or current, which is reflected
on the transmission line 232, to determine whether the voltage or
current is greater than a second pre-determined value. When the
voltage or current is greater than the second pre-determined value,
the comparator provides the first signal to the DSP 150 and when
the voltage or current is not greater than the second
pre-determined value, the comparator provides the second signal to
the DSP 150. In response to receiving the first signal during the
state S0 of the TTL signal 106, the DSP 150 identifies that the
voltage or current is greater than the second pre-determined value
and in response to receiving the second signal during the state S0
of the TTL signal 106, the DSP 150 identifies that the voltage or
current does not exceed the second pre-determined value. When the
DSP 150 determines that the voltage or current exceeds the second
pre-determined value, the DSP 150 determines the frequency value
F20 corresponding to the second pre-determined value and provides
the frequency value F20 to the AFT 120. Moreover, upon receiving
the indication that the voltage or current exceeds the second
pre-determined value, DSP 150 determines the power value P20
corresponding to the second pre-determined value and provides the
power value P20 to the power controller 154. In an embodiment, a
comparator includes analog circuitry, e.g., one or more operational
amplifiers.
[0085] FIG. 2 is an embodiment of a table 250 showing a change in
states based on whether a gamma value is greater than the first
threshold or the second threshold. As indicated in the table 250,
the TTL signal 112 is used to provide a digital pulsed signal,
e.g., a clock signal, to the DSP 140 (FIG. 1).
[0086] When the TTL signal 112 is in the state S1, the 2 MHz signal
has the high power level. During the state S1 of the TTL signal
112, it is determined whether a gamma value exceeds the first
threshold. In response to determining that the gamma value exceeds
the first threshold, power value of the 60 MHz signal is changed to
the power value P20 from the power value P21 and the frequency
value of the 60 MHz signal is changed from the frequency value F20
to the frequency value F21 to achieve a state S1.
[0087] Also, when the TTL signal 112 is in the state S0, the 2 MHz
signal has the low power level. During the state S0 of the TTL
signal 112, it is determined whether a gamma value exceeds the
second threshold. In response to determining that the gamma value
exceeds the second threshold, power value of the 60 MHz signal is
changed to the power value P21 from the power value P20 and the
frequency value of the 60 MHz signal is changed from the frequency
value F21 to the frequency value F20 to achieve a state S0.
[0088] FIG. 3 shows an embodiment of a graph 111, which is a plot
of a forward power versus time of two RF signals, the 2 MHz signal
and the 60 MHz signal during the training routine. In an
embodiment, the training routine is performed once to determine
tuned RF values, e.g., the power values P20 and P21, the frequency
values F20 and F21, the threshold values, etc., or performed once
during a time period to account for, for example, plasma impedance.
In this example, the 2 MHz signal is an independently pulsing (IP)
RF signal and the 60 MHz signal represents a dependent RF signal
that tunes its RF frequency to optimize power delivery when the 2
MHz RF signal pulses. Although only one dependent RF generator
(e.g., 60 MHz) is discussed in connection with FIG. 3, it should be
understood that there may be multiple dependent RF generators, each
of which may undergo a similar training routine to ascertain its
own optimal tuned RF frequencies and thresholds when the IP RF
signal pulses.
[0089] FIG. 3 may be better understood when studied in conjunction
with an embodiment of a flowchart of a method 113, which is
described with reference to FIG. 4. The method 113 is an example of
the training routine.
[0090] At a point 115, an IP RF signal 119 of the IP RF generator
(e.g., 2 MIIz generator) is pulsed high to a high power set point.
In the example of FIG. 1, the high power set point for the 2 MHz IP
RF generator is 6 kilowatts (kW). This is also shown in an
operation 117 of FIG. 4.
[0091] Further, the dependent RF generator (e.g., 60 MHz generator)
is set to its frequency self-tuning mode to allow the dependent RF
generator to converge to an optimal RF frequency for power delivery
when the IP RF signal 119 is pulsed high. This is also shown in the
operation 117 of FIG. 4. To elaborate, the independent or dependent
RF generator monitors many variables associated with the plasma
chamber 102 and adjusts its own variables to maximize power
delivery to the plasma chamber 102. The independent or dependent RF
generator then tunes its RF signal frequency to minimize gamma,
thereby maximizing power delivery efficiency.
[0092] The IP RF signal of 2 MHz is pulsed high during the period
between points 115 and 121. This high pulse duration of the IP RF
signal is greatly extended during the training time, e.g., from
tenths of seconds up to multiple of seconds relative to an IP RF
signal high pulse duration employed during production time for
processing of the substrate 108. The substrate 108 may be processed
to etch the substrate 108, to deposit one or more layers on the
substrate 108, to clean the substrate 108, etc. This artificially
extended high pulse duration gives the dependent RF generator
enough time to optimally tune its frequency to maximize power
delivery efficiency for the plasma impedance condition that exists
when the IP RF signal is pulsed high.
[0093] The dependent RF generator tunes to a frequency value of
61.3 MHz for a gamma value of 0.04 when the 2 MHz IP RF signal
pulses high. This optimal tuned RF frequency of 61.3 MHz, e.g.,
IDPC_Freq1, for the dependent RF generator is then recorded within
the AFT 118 (FIG. 1) as illustrated in operation 123 and is set as
the IDPC_Freq1 as illustrated in an operation 125 of FIG. 4. The
IDPC_Freq1 is an example of the frequency value F21. Forward power,
e.g., 6 kW, etc., sensed by the sensor 212 at the frequency
IDPC_Freq1 is an example of the power value P21. This 61.3 MHz
value represents the optimal RF frequency for the 60 MHz dependent
RF signal when the 2 MHz IP RF signal pulses high. The gamma value
of 0.04 verifies that power delivery is efficient at this optimal
tuned RF frequency for the dependent RF generator.
[0094] The dependent RF generator is then operated in the fixed
frequency mode whereby its RF frequency is not allowed to tune.
Instead, the dependent RF generator is forced to operate at the
aforementioned 61.3 MHz optimal tuned RF frequency and the 2 MHz IP
RF signal transitions from its high power set point to its low
power set point (from 121 to 127). This can be seen in an operation
131 of FIG. 4. Although the low power set point for the 2 MHz RF
signal is zero in the example of FIG. 2, in an embodiment, the low
power set point may be any power level setting that is lower than
the high power set point of 6 kW.
[0095] After the IP RF signal pulses low (after point 127), the
previous optimal tuned RF frequency of 61.3 MHz is no longer
efficient RF frequency for power delivery by the dependent RF
generator. This is because the plasma impedance has changed when
the 2 MHz IP RF signal pulses low to deliver a lower amount of RF
power to the plasma within the plasma chamber 102. The inefficiency
is reflected in a gamma value of 0.8, which is detected by the
sensor 212 of the dependent RF generator. This gamma value of 0.8
is recorded in an operation 133 of FIG. 4 and may be set as an
IDPC_Gamma1 threshold in an operation 135 of FIG. 4. The
IDPC_Gamma1 threshold is an example of the second threshold. The
IDPC_Gamma2 threshold is stored within a memory device of the
DSP150, a memory device of the AFT 120, and/or a memory device of
the power controller 154 (FIG. 1).
[0096] During production time, as the IP RF signal is pulsed high
and the 60 MHz RF signal is at 61.3 MHz and the IDPC_Gamma1
threshold is subsequently encountered, the dependent RF generator
determines that the 2 MHz IP RF signal has just transitioned from
high to low.
[0097] In one or more embodiments, the IDPC_Gamma1 threshold can be
adjusted for sensitivity by a Threshold 1 Adjust value. For
example, it may be desirable to set in the operation 135 the
IDPC_Gamma1 threshold at 0.7 instead of 0.8, e.g., slightly below a
gamma value that exists due to the high-to-low transition of the 2
MHz IP RF signal, to increase the high-to-low detection sensitivity
by the sensor 212. In this example, the Threshold 1_Adjust value is
-0.1, and the IDPC_Gamma 1 threshold of 0.7 is the sum of the gamma
value of 0.8 and the Threshold I Adjust value of -0.1.
[0098] Once the IDPC_Gamma1 threshold is obtained, the 60 MHz
dependent RF generator is set to the frequency self-tuning mode in
an operation 139 to enable the 60 MHz dependent RF generator to
determine an optimal tuned RF frequency for power delivery when the
2 MHz IP RF signal pulses low. Again, the low pulse of the 2 MHz IP
RF signal is artificially extended between points 127 and 137 of
FIG. 3 to enable both an ascertainment of the IDPC_Gamma 1
threshold and to permit the 60 MHz dependent RF generator to
self-tune to an optimal RF frequency for power delivery during the
low pulse of the 2 MHz IP RF signal.
[0099] Once the dependent RF generator tunes to the optimal RF
frequency, e.g., 60.5 MHz, for power delivery during the low pulse
of the 2 MHz IP RF signal, the optimal tuned RF frequency of the
dependent RF generator is recorded in an operation 141 and is set
as IDPC Freq 2 in an operation 143.
[0100] After the dependent RF generator has tuned to its optimal RF
frequency value, e.g., 60.5 MHz, etc., for the low pulse of the 2
MHz IP RF signal, the dependent RF generator is set to operate in a
fixed frequency mode in an operation 145 at an IDPC_Freq2 and the 2
MHz IP RF generator is allowed to pulse high, e.g., transition from
the point 137 to a point 147. The IDPC_Freq2 is an example of the
frequency value F20. Forward power sensed by the sensor 212 at the
frequency IDPC_Freq2 is an example of the power value P20. This can
also be seen in the operation 145 of FIG. 4.
[0101] After the 2 MHz IP RF signal pulses high, e.g., after point
137, the previous optimal tuned RF frequency IDPC_Freq2 is no
longer the efficient RF frequency for power delivery by the 60 MHz
RF generator. This is because the plasma impedance has changed when
the 2 MHz independently pulsing RF signal pulses high to deliver a
higher amount of RF power to the plasma within the plasma chamber
102. The inefficiency is reflected in a gamma value of 0.78, which
is detected by the sensor 212. This gamma value of 0.78 is recorded
in an operation 151 and may be set as an IDPC_Gamma2 threshold in
an operation 153. THE IDPC_Gamma2 threshold is an example of the
first threshold. The IDPC_Gamma2 threshold is stored within a
memory device of the DSP 150, a memory device of the AFT 118,
and/or a memory device of the power controller 152.
[0102] During production time as the IP RF signal is pulsed low and
the 60 MHz RF signal is at 60.5 MHz, which is the optimal tuned RF
frequency for the 60 MHz RF generator when the IP RF signal is
pulsed low, and the IDPC_Gamma2 threshold is subsequently
encountered, the dependent RF generator determines that the 2 MHz
IP RF signal has just transitioned from low to high.
[0103] In one or more embodiments, the IDPC_Gamma2 threshold can be
adjusted for sensitivity by a Threshold2 Adjust value. For example,
it may be desirable to set at the operation 153 of FIG. 4 the
IDPC_Gamma2 threshold at 0.75 instead of 0.78, e.g., slightly below
the true gamma value that exists due to the low-to-high transition
of the 2 MHz IP RF signal, to increase the low-to-high detection
sensitivity by the sensor 212. In this example, the
Threshold2_Adjust value is -0.03, and the IDPC Gamma2 threshold of
0.75 is the sum of the gamma value of 0.78 and the Threshold2
Adjust value of -0.03.
[0104] The two optimal tuned RF frequencies values, e.g., 61.3 MHz
and 60.5 MHz, and the two gamma threshold values, e.g., IDPC_Gamma1
threshold and IDPC_Gamma2 threshold, are then employed during
production time when the 2 MHz is allowed to pulse and the 60 MHz
dependent RF generator flips back and forth between the two
previously learned optimal tuned RF frequencies when the sensor 212
detects that a gamma value has exceeded the thresholds. The 60 MHz
signal is illustrated as a signal 155 in FIG. 3.
[0105] FIG. 5 is a diagram of an embodiment of a system 262 for
changing a state based on plasma impedance, where the power
controllers and/or the frequency tuners do not provide non-zero
values. The system 262 is similar to the system 180 of FIG. 1
except that the system 262 includes a power controller 172 and an
AFT 264, each of which provide non-zero values.
[0106] The DSP 140 provides the identified state S0 from a
corresponding memory location to the AFT 264 and to the power
controller 172. As an example, the DSP 140 indicates to the AFT 264
and the power controller 172 that the TTL signal 112 is in the
state S0 between times t2 and t3 of a duty cycle. The AFT 264
determines a frequency value based on a state of the TTL signal 112
and the power controller 172 determines a power value based on the
state of the TTL signal 112. For example, the AFT 264 determines
that a frequency value F10 is to be provided to the 2 MHz DA system
when the state of the TTL signal 112 is S0 and the power controller
172 determines that a power value P10 is to be provided to the 2
MHz DA system when the state of the TTL signal 112 is S0. In one
embodiment, the values F10 and P10 are positive values.
[0107] The frequency value F10 is stored in the AFT 264 and the
power value P10 is stored in the power controller 172. When the
state of the TTL signal 112 is S0, the power controller 172
provides the power value of P10 to the 2 MHz DA system and the AFT
264 provides the frequency value of F10 to the 2 MHz DA system.
[0108] The 2 MHz DA system receives the frequency value of F10 and
the power value of P10 during the state S0. Upon receiving the
values F10 and P10, the 2 MHz DA system generates RF power at the
frequency F10 and the RF power has the power value of P10. The
amplifier of the 2 MHz DA system supplies forward power having a
power value that is proportional to the power value P10 and having
the frequency value F10 via the transmission line 230 and the
impedance matching circuit 182 to the plasma chamber 102.
[0109] In an embodiment, during the state S0 of the TTL signal 112,
the AFT 264 determines a frequency value based on the value of
gamma received from the DSP 140. During the state S0, the AFT 264
adjusts the frequency value of F10 based on the frequency value
that is generated from the gamma value and provides the adjusted
frequency value to the 2 MHz DA system. Moreover, during the state
S0, the power controller 172 determines a power value based on the
value of gamma received from the DSP 140. During the state S0, the
power controller 172 adjusts the power value of P10 based on the
power value that is generated based on the gamma value and provides
the adjusted power value to the 2 MHz DA system. Also, during the
state S0, the 2 MHz DA system generates a power signal having the
adjusted frequency value received from the AFT 264 and having the
adjusted power value received from the power controller 172, and
supplies the power signal via the impedance matching circuit 182 to
the plasma chamber 102.
[0110] The power controllers 142 and 172, the AFTs 114 and 264, and
the DSP 140 are parts of a generator controller 290. The generator
controller 290, the ADC 220, the sensor 210, and the 2 MHz DA
system are parts of a 2 MHz generator 292.
[0111] In one embodiment, instead of each DSP 140 or 150, any
number of processors are used to perform the functions performed by
the DSP.
[0112] FIG. 6A shows embodiments of graphs 302, 304, 306, and 308.
Each graph 302, 304, 306, and 308 plots power values in kilowatts
(kW) as a function of time t. As indicated in graph 302, a 2 MHz
power signal, which is a power signal supplied by the 2 MHz DA
system has a power value of a1 during the state S1 and has a power
value of 0 during the state S0. The power value a1 is an example of
the power value P11. Also, a 60 MHz power signal, which is a power
signal supplied by the 60 MHz DA system has a power value of a2
during the state S1 and has a power value of a3 during the state
S0. The power value of a2 is an example of the power value P21 and
the power value of a3 is an example of the power value P20.
[0113] As indicated in the graph 304, the 60 MHz power signal has
the power value a2 during states S1 and S0. Moreover, as indicated
in graph 306, the 2 MHz signal has a power value of a4 during the
state S0. The power value a4 is an example of the power value P10.
As indicated in graph 308, the 60 MHz signal has the power value of
a2 when the 2 MHz signal has the power value of a4.
[0114] FIG. 6B shows embodiments of graphs 310, 312, 314, and 316.
Each graph 310, 312, 314, and 316 plots power values in kilowatts
as a function of time t. As shown in graph 310, instead of the 60
MHz signal transitioning from the power value of a2 to the power
value of a3 (FIG. 6A), the 60 MHz signal transitions from the power
value of a2 to a power value of zero.
[0115] Moreover, as shown in graph 312, the 60 MHz signal
transitions from the power value of a2 to a power value of a5,
which is an example of the power value P20. As shown in graph 314,
the 60 MHz signal has the power value of zero during the state S0
when the 2 MHz signal has a non-zero power value of a4. As shown in
graph 316, the 60 MHz power signal has a non-zero power value of a5
during the state S0 when the 2 MHz signal has a non-zero power
value of a4.
[0116] FIG. 7A shows embodiments of graphs 318, 320, 322, and 324.
Each graph 318, 320, 322, and 324 plots power values in kilowatts
as a function of time t. Graph 318 is similar to graph 302 (FIG.
6A), graph 320 is similar to graph 304 (FIG. 6A), graph 320 is
similar to graph 306 (FIG. 6A), and graph 322 is similar to graph
308 (FIG. 6A) except that the graphs 318, 320, 322, and 324 include
a plot of a 27 MHz signal. The 27 MHz signal is generated from a 27
MHz DA system (not shown) of the 27 MHz generator. The 27 MHz
signal is an RF signal having a power value of a6 during both
states S1 and S0.
[0117] FIG. 7B shows embodiments of graphs 326, 328, 330, and 332.
Each graph 326, 328, 330, and 332 plots power values in kilowatts
as a function of time t. Graph 326 is similar to graph 310 (FIG.
6B), graph 328 is similar to graph 312 (FIG. 6B), graph 330 is
similar to graph 314 (FIG. 6B), and graph 332 is similar to graph
316 (FIG. 6B) except that the graphs 326, 328, 330, and 332 include
a plot of a 27 MHz signal that has the power value of a6.
[0118] FIG. 7C shows embodiments of graphs 334, 336, 338, and 340.
Each graph 334, 336, 338, and 340 plots power values in kilowatts
as a function of time t. Graph 334 is similar to graph 302 (FIG.
6A), graph 336 is similar to graph 304 (FIG. 6A), graph 338 is
similar to graph 306 (FIG. 6A), and graph 340 is similar to graph
308 (FIG. 6A) except that the graphs 334, 336, 338, and 340 include
a plot of a 27 MHz signal. The 27 MHz signal transitions from
having a power value of a7 during the state S1 to having a power
value of a8 during the state S0. The power value a7 is less than
the power value a8.
[0119] FIG. 7D shows embodiments of graphs 342, 344, 346, and 348.
Each graph 342, 344, 346, and 348 plots power values in kilowatts
as a function of time t. Graph 342 is similar to graph 310 (FIG.
6B), graph 344 is similar to graph 312 (FIG. 6B), graph 346 is
similar to graph 314 (FIG. 6B), and graph 348 is similar to graph
316 (FIG. 6B) except that the graphs 342, 344, 346, and 348 include
a plot of a 27 MHz signal that has the power values of a7 and
a8.
[0120] FIG. 7E shows embodiments of graphs 350, 352, 354, and 356.
Each graph 350, 352, 354, and 356 plots power values in kilowatts
as a function of time t. Graph 350 is similar to graph 302 (FIG.
6A), graph 352 is similar to graph 304 (FIG. 6A), graph 354 is
similar to graph 306 (FIG. 6A), and graph 356 is similar to graph
308 (FIG. 6A) except that the graphs 350, 352, 354, and 356 include
a plot of a 27 MHz signal. The 27 MHz signal transitions from
having a power value of a9 during the state S1 to having a power
value of a10 during the state S0. The power value a9 is greater
than the power value a10.
[0121] FIG. 7F shows embodiments of graphs 358, 360, 362, and 364.
Each graph 358, 360, 362, and 364 plots power values in kilowatts
as a function of time t. Graph 358 is similar to graph 310 (FIG.
6B), graph 360 is similar to graph 312 (FIG. 6B), graph 362 is
similar to graph 314 (FIG. 6B), and graph 364 is similar to graph
316 (FIG. 6B) except that the graphs 358, 360, 362, and 364 include
a plot of a 27 MHz signal that has the power values of a9 and
a10.
[0122] It should be noted that in the graphs 302, 304, 306, 308,
310, 312, 314, 316, 318, 320, 322, 324, 326, 328, 330, 332, 334,
336, 338, 340, 342, 344, 346, 348, 350, 352, 354, 356, and 358
shown above, the 2 MHz signal is shown as a solid line, the 60 MHz
signal is shown as a dashed line, and the 27 MHz signal is shown as
a dotted line.
[0123] FIG. 8 is a block diagram of an embodiment of a system 310
for selecting between AFTs 118 and 120 (FIGS. 1 and 3) based on
whether a gamma value is greater than the first threshold or the
second threshold. When the TTL signal 112 is in the state S1 and a
gamma value measured during the state S1 exceeds the first
threshold, a select logic 128, which is an example of a selector,
of the system 310 selects the AFT 118 and when the TTL signal 112
is in the state S0 and a gamma value measured during the state S0
exceeds the second threshold, the select logic 128 selects the AFT
120. Examples of the select logic 128 include a multiplexer. When
the select logic 128 includes the multiplexer, a signal indicating
that a gamma value measured during the state S1 of the TTL signal
112 is greater than the first threshold or a signal indicating that
a gamma value measured during the state S0 of the TTL signal 112 is
greater than the second threshold is received at a select input of
the multiplexer. The DSP 150 generates a signal indicating a gamma
value measured during the state S1 of the TTL signal 112 is greater
than the first threshold and provides the signal to the multiplexer
when the TTL signal 112 has the state S1. The DSP 150 generates a
signal indicating that a gamma value measured during the state S0
of the TTL signal 112 is greater than the second threshold and
provides the signal to the multiplexer when the TTL signal 112 has
the state S0.
[0124] In one embodiment, the select logic 128 includes a
processor. In an embodiment, the select logic 128 is implemented
within the DSP 140.
[0125] When the AFT 118 is selected, the AFT 118 provides the
frequency value F21 to the 60 MHz DA system. Similarly, when the
AFT 120 is selected, the AFT 120 provides the frequency value F20
to the 60 MHz DA system.
[0126] The 60 MHz DA system generates the 2 MHz signal synchronous
with a clock signal that is received from a clock source 312. In
one embodiment, the clock signal of the clock source 312 is
asynchronous with the TTL signal 112. In an embodiment, the clock
signal of the clock source 3112 is synchronous with the TTL signal
112.
[0127] In one embodiment, the select logic 128 selects between the
power controllers 152 and 154 (FIG. 5) instead of the AFTs 118 and
120. When the power controller 152 is selected during the state S1
of the TTL signal 112, the power controller 152 provides the power
value P21 to the 60 MHz DA system and when the power controller 154
is selected ruing the state S0 of the TTL signal 112, the power
controller 154 provides the power value P20 to the 60 MHz DA
system.
[0128] In one embodiment, the select logic 128 is implemented
within the 27 MHz generator in a similar manner in which the select
logic 128 is implemented within the 60 MHz generator 276 (FIGS. 1
and 3).
[0129] A value of gamma is transferred by the select logic 128 to
AFT 118 or 120 based on the state S1 or S0. For example, when the
state is S1, the DSP 150 provides the first gamma value to the
select logic 128. In this example, the select logic 128 that has
selected the AFT 118 during the state S1 transfers the first gamma
value received from the DSP 150 to the AFT 118. As another example,
when the state is S0, the DSP 150 provides the second gamma value
to the select logic 128. In this example, the select logic 128 that
has selected the AFT 120 during the state S0 transfers the second
gamma value received from the DSP 150 to the AFT 120.
[0130] Similarly, in the embodiments in which the power controllers
152 and 154 (FIG. 5) are used, the select logic 128 transfers the
first gamma value received from the DSP 150 to the power controller
152 during the state S1 and transfers the second gamma value
received from the DSP 150 to the power controller 154.
[0131] Furthermore, in the embodiment in which the select logic 128
is implemented within the 27 MHz generator and is coupled to power
controllers of the 27 MHz generator, the select logic 128 transfers
a third gamma value received from a DSP of the 27 MHz generator to
one of the power controllers during the state S1 and transfers a
fourth gamma value received from the DSP to another one of the
power controllers during the state S0. In this embodiment, the
third gamma value is generated based on the forward and reflected
powers on a transmission line that is coupled to the 27 MHz
generator. Also, in this embodiment, both the forward reflected
powers are sensed by a sensor of the 27 MHz generator. In this
embodiment, the fourth gamma value is generated based on the
forward and reflected powers on the transmission line that is
coupled to the 27 MHz generator.
[0132] Moreover, in the embodiment in which the select logic 128 is
implemented within the 27 MHz generator and is coupled to AFTs of
the 27 MHz generator, the select logic 128 transfers the third
gamma value received from the DSP of the 27 MHz generator to one of
the AFTs during the state S1 and transfers the fourth gamma value
received from the DSP to the other one of the AFTs during the state
S0.
[0133] FIG. 9 is a flowchart of an embodiment of a method 321 for
adjusting a frequency and/or power of the 60 MHz DA system to
achieve state S1 or S0 of the 60 MHz generator 276 (FIGS. 1 and 3).
In an operation 325, plasma is struck, e.g., generated, within the
plasma chamber 102 (FIG. 1).
[0134] In an operation 327, during both states of the TTL signal
112, forward and reflected powers on the transmission line 232 are
measured by the sensor 212 (FIG. 5). The measured forward and
reflected powers are converted from an analog format into a digital
format.
[0135] In an operation 329, the DSPs 140 and 150 calculate gamma
values from the digital values of the forward and reflected powers
measured during the states S0 and S1 of the TTL signal 112. For
each state of the TTL signal 112, a gamma value is determined by a
DSP. For example, during the state S0 of the TTL signal 112, a
gamma value is determined by the DSP 150 based on a relationship
between the forward and reflected power, e.g., a square root of a
ratio of reflected power to forward power sensed on the
transmission line 232, etc., and during the state S1 of the TTL
signal 112, a gamma value is determined by the DSP 150 based on a
relationship between the forward and reflected power, e.g., a
square root of a ratio of reflected power to forward power sensed
on the transmission line 232 (FIG. 5).
[0136] In an operation 331, it is determined whether a gamma value
measured during the state S1 of the TTL signal 112 is greater than
the first threshold and it is determined whether a gamma value
measured during the state S0 of the TTL signal 112 is greater than
the second threshold. For example, the AFT 118 and the power
controller 152 determine whether a gamma value received from the
DSP 150 is greater than the first threshold and the AFT 120 and the
power controller 154 determine whether a gamma value received from
the DSP 150 exceeds the second threshold. As another example, the
DSP 150 determines whether the first gamma value is greater than
the first threshold or the second gamma value is greater than the
second threshold.
[0137] Upon determining that the gamma value is greater than the
first threshold, in an operation 333, the AFT 118 provides the
frequency value F21 to the 60 MHz DA system and the power
controller 152 provides the power value P21 to the 60 MHz DA
system. Moreover, upon determining that the gamma value is greater
than the second threshold, in an operation 335, the AFT 120
provides the frequency value F20 to the 60 MHz DA system and the
power controller 154 provides the power value P20 to the 60 MHz DA
system. The operation 327 of the method 321 repeats after the
operations 333 and 335.
[0138] Although the method 321 is described with respect to the 60
MHz generator 276, in one embodiment, the method 321 applies to the
27 MHz generator or a generator with a frequency other than 27 MHz
or 60 MHz.
[0139] FIG. 10 shows an embodiment of a graph 400 of normalized RF
variables versus time for implementing RF tuning by the dependent
RF generator for optimal production time power delivery during IP
RF signal pulsing. Examples of the normalized RF variables include
forward power and gamma values. FIG. 10 may be better understood
when studied in conjunction with a flowchart of a method 500, an
embodiment of which is shown in FIG. 11. The method 500 provides
details regarding operations for implementing frequency tuning by
the dependent RF generator for optimal power delivery during
pulsing.
[0140] At a point 402, the 2 MHz IP RF generator is pulsed high and
the 60 MHz dependent RF generator is set to its previously learned
optimal RF frequency of IDPC_Freq1 (e.g., 61.3 MHz) or allowed to
self-tune to this optimal RF frequency of IDPC_Freq1. This is seen
in an operation 504 of FIG. 11. Thereafter, the dependent RF
generator operates in the frequency tuning mode.
[0141] In the example of FIG. 10, the 2 MIIz IP RF signal pulses at
a pulsing frequency of 159.25 Hz with a 50% duty cycle, which may
vary if desired, between a high power set point of 6 kW and a low
power set point of 0 kW, which is not a requirement and can be
non-zero. The 60 MHz dependent RF generator provides power at a
power set point of 900 W. While the 60 MHz dependent RF generator
delivers power to the plasma load within the plasma chamber 102,
the dependent RF generator also monitors the gamma value via the
sensor 212 as illustrated in operations 506 and 508 of FIG. 11.
[0142] At a point 404, the 2 MHz IP RF signal pulses low to a point
409. Shortly after this high-to-low transition, a gamma value
measured by the 60 MHz dependent RF generator spikes from around
0.04 to around 0.8, e.g, from a point 407 to a point 408. If the
IDPC_Gamma1 threshold is set at, e.g., 0.7, an excursion by the
detected gamma value (branch YES of the operation 508) facilitates
the 60 MHz RF generator to flip from one previously learned optimal
tuned RF frequency value of IDPC_Freq1 to the other previously
learned optimal tuned RF frequency value of IDPC_Freq2. This is
seen in an operation 510 of FIG. 11. This tuning of the 60 MHz
dependent RF generator from IDPC_Freq1 to IDPC_Freq2 in response to
the high-to-low transition of the 2 MHz IP RF signal achieves a
measured gamma value down to 0.05, e.g., from the point 410 to a
point 412.
[0143] At a point 415, the 2 MHz IP RF signal pulses from low to
high, e.g., reaches a point 417. Shortly after this low-to-high
transition, a gamma value is measured in operations 512 and 514 by
the dependent RF generator spikes from around 0.05 to around 0.78.
The spike is illustrated between points 414 and 416.
[0144] If the IDPC_Gamma2 threshold is set at to trip at, for
example, 0.75, the excursion by the detected gamma value, e.g., a
YES branch of an operation 514 of FIG. 11, facilitates the 60 MHz
RF generator to flip from the previously learned optimal tuned RF
frequency value IDPC_Freq2 to the other previously learned optimal
tuned RF frequency value of IDPC_Freq1. This is seen in the
operation 504 of FIG. 11. This tuning of the 60 MHz dependent RF
generator from IDPC_Freq2 to IDPC_Freq1 in response to the
low-to-high transition of the 2 MHz IP RF signal brings the
measured gamma value down to 0.04, e.g., from the point 418 to a
point 420.
[0145] It should be noted that the time scale of FIG. 10 reflects a
faster time scale than that of FIG. 3. The time scale of FIG. 10
illustrates production time and the time scale of FIG. 3
illustrates learning time. This is the case when, as mentioned, the
high duration and the low duration of the IP RF pulse are
artificially extended during learning time to permit the dependent
RF generator to self-tune to the optimal tune RF frequencies for
learning purposes. It should further be noted that the 60 MHz
signal is illustrated as a signal 460 in FIG. 10.
[0146] In one embodiment, during production time, such self-tuning
is not used since the dependent RF generator operates essentially
as a state machine and flips from one learned optimal RF frequency
to another learned optimal RF frequency as it detects the
high-to-low transition of the IP RF signal and the low-to-high
transition of the IP RF signal. The high-to-low transition is
detected by comparing a measured gamma value to the IDPC_Gamma1
threshold and by determining the previous state of the IP RF signal
prior to the detection of the gamma excursion. Moreover, the
low-to-high transition is detected by comparing the measured gamma
value versus the IDPC_Gamma2 threshold and by determining the
previous state of the IP RF signal prior to the detection of the
gamma excursion.
[0147] It should be noted that although the above-described
embodiments relate to providing the 2 MHz RF signal and/or 60 MHz
signal and/or 27 MHz signal to the lower electrode 104 and
grounding the upper electrode 110, in several embodiments, the 2
MHz, 60 MHz, and 27 MHz signals are provided to the upper electrode
110 while the lower electrode 104 is grounded.
[0148] It is also noted that in one embodiment, an input, e.g.,
frequency input, power input, etc., or a level, e.g., power level,
frequency level, includes one or more values that are within a
limit, e.g., standard deviation, etc., of another value. For
example, a power level includes the power value P21 and other power
values that are within the limit of the power value P21. In this
example, the power level excludes any power values for another
state, e.g., power value P20 for state S0. As another example, a
frequency input includes the frequency value F11 and other
frequency values that are within a limit of the frequency value
F11. In this example, the frequency input excludes any frequency
values for another state, e.g., frequency value F10 for state
S0.
[0149] It is noted that although the above-described embodiments
are described with reference to parallel plate plasma chamber, in
one embodiment, the above-described embodiments apply to other
types of plasma chambers, e.g., a plasma chamber including an
inductively coupled plasma (ICP) reactor, a plasma chamber
including an electron-cyclotron resonance (ECR) reactor, etc. For
example, the 2 MHz and the 60 MHz power supplies are coupled to an
inductor within the ICP plasma chamber.
[0150] Moreover, although some of the above embodiments are
described using gamma values, in an embodiment, impedance
difference values can be used. For example, when the state of the
TTL signal 112 is S1, the DSP 150 determines an impedance from
reflected power over the transmission line 232 and also determines
an impedance from forward power over the transmission line 232. The
DSP 150 determines whether a first difference between the
impedances exceeds a first limit and upon determining so, sends a
signal indicating so and also indicating a value of the first
difference. Upon receiving the signal indicating the value of the
first difference, the AFT 118 retrieves from a memory device the
frequency value F21 and the power controller 152 retrieves from a
memory device the power value P21. The values F21 and P21 are then
provided to the 60 MHz DA system.
[0151] Similarly, when the state of the TTL signal 112 is S0, the
DSP 150 determines an impedance from reflected power over the
transmission line 232 and also determines an impedance from forward
power over the transmission line 232. The DSP 150 determines
whether a second difference between the impedances exceeds a second
limit and upon determining so, sends a signal indicating so and
also indicating a value of the second difference. Upon receiving
the signal indicating the value of the second difference, the AFT
120 retrieves from a memory device the frequency value F20 and the
power controller 154 retrieves from a memory device the power value
P20. The values F20 and P20 are then provided to the 60 MHz DA
system.
[0152] In one embodiment, the operations performed by an AFT and/or
a power controller of a generator controller are performed by a DSP
of the generator controller. For example, the operations, described
herein, as performed by the AFT 118 and 120 are performed by the
DSP 150.
[0153] In an embodiment, the terms "driver and amplifier" and "DA
system" are used interchangeably herein.
[0154] Embodiments described herein may be practiced with various
computer system configurations including hand-held devices,
microprocessor systems, microprocessor-based or programmable
consumer electronics, minicomputers, mainframe computers and the
like. The embodiments can also be practiced in distributed
computing environments where tasks are performed by remote
processing devices that are linked through a network.
[0155] With the above embodiments in mind, it should be understood
that the embodiments can employ various computer-implemented
operations involving data stored in computer systems. These
operations are those requiring physical manipulation of physical
quantities. Any of the operations described herein that form part
of the embodiments are useful machine operations. The embodiments
also relates to a device or an apparatus for performing these
operations. The apparatus may be specially constructed for a
special purpose computer. When defined as a special purpose
computer, the computer can also perform other processing, program
execution or routines that are not part of the special purpose,
while still being capable of operating for the special purpose.
Alternatively, the operations may be processed by a general purpose
computer selectively activated or configured by one or more
computer programs stored in the computer memory, cache, or obtained
over a network. When data is obtained over a network the data may
be processed by other computers on the network, e.g., a cloud of
computing resources.
[0156] One or more embodiments can also be fabricated as
computer-readable code on a non-transitory computer-readable
medium. The non-transitory computer-readable medium is any data
storage device that can store data, which can be thereafter be read
by a computer system. Examples of the non-transitory
computer-readable medium include hard drives, network attached
storage (NAS), ROM, RAM, compact disc-ROMs (CD-ROMs),
CD-recordables (CD-Rs), CD-rewritables (CD-RWs), magnetic tapes and
other optical and non-optical data storage devices. The
non-transitory computer-readable medium can include
computer-readable tangible medium distributed over a
network-coupled computer system so that the computer-readable code
is stored and executed in a distributed fashion.
[0157] Although the method operations in the flowcharts above were
described in a specific order, it should be understood that other
housekeeping operations may be performed in between operations, or
operations may be adjusted so that they occur at slightly different
times, or may be distributed in a system which allows the
occurrence of the processing operations at various intervals
associated with the processing, as long as the processing of the
overlay operations are performed in the desired way.
[0158] One or more features from any embodiment may be combined
with one or more features of any other embodiment without departing
from the scope described in various embodiments described in the
present disclosure.
[0159] Although the foregoing embodiments have been described in
some detail for purposes of clarity of understanding, it will be
apparent that certain changes and modifications can be practiced
within the scope of the appended claims. Accordingly, the present
embodiments are to be considered as illustrative and not
restrictive, and the embodiments are not to be limited to the
details given herein, but may be modified within the scope and
equivalents of the appended claims.
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